SuperP4: Handling cases where variables are of the same name as built in functions

[kaarthikalagappan]

There can exist a case where a built in header function's values can be controlled by a manually defined variable of same name. Right now ignoring the variable declaration (not adding it to the symbol table, so only the default function of the same name exists). Need to check the correlation between the defined variable and the default function of the same name.

Latest commit in branch: 0fde6f5

Example (issue1717.p4 in p4c test suite):

header H {
    bit<32> isValid;
}

header H1 {
    bit<16> f;
    bit<8> minSizeInBytes;
    bit<8> minSizeInBits;
    T f1;
    E e;
}

isValid() is a built in function of headers, similar for minSizeInBytes and minSizeInBits